乾燥砂土中音波及振波之傳遞特性

The transmission properties of sound waves and vibration waves in dry sand

張哲胤(Che-yin Chang)

指導教授 ： 張惠文

國立中央大學/工學院/土木工程學系/碩士(2007年)

摘要

本研究主要係利用微音器及加速度計量得之波傳訊號，對砂土層中因振動或變位所產生之音波與振波之傳播特性，進行探討與測試。
本研究規劃在大型土槽中挖出一溝槽，再將挖出之砂依所需之相對密度進行霣降，霣降過程中將微音器及加速度計置於所需之各種位置，量測由音源傳遞至微音器處的音波訊號反應，經由處理得到音速、均方根音壓及頻率等，加速度計擺放位置同微音器，利用加速度計獲得之數據，探討聲音是否能藉由振動進行傳遞，並與微音器之數據進行比較。結果顯示波速部分在深度 10至 40cm之範圍內，音速介於 160至 210m/s之間，隨深度增加，速度隨之增加。均方根音壓的變化在敲擊試驗中，在超過距音源 45cm之後，微音器接收之訊號以非常緩慢的速度衰減，而加速度計測得訊號亦是如此。另外，本研究進行了對照之發聲試驗。音源的產生，係利用揚聲器播放，但音波並沒有大幅擾動砂土。發聲試驗之音源來自敲擊試驗之音源經錄製後由揚聲器播放，結果顯示發聲試驗中音波在砂土層傳播很快就會消散，在距音源 30cm後，幾無傳遞能量。說明當土層發生變位或錯動時，只要振動的量夠大，音波便能藉由振波向外傳遞至較遠處。

關鍵字

振波 ； 音波 ； 音速 ； 均方根音壓 ； 波傳

並列摘要

This research used wave signals measured from microphones and accelerometers to investigate transmission properties of sound waves and vibration waves generated by shock vibration or shear displacement in sand layer.
This research excavated a trench in the large testing pit, then pluviated sand into the trench with planned relative densities. Microphones and accelerometers were embedded in the prearranged locations during sand pluviation. Signals of sound waves and vibrations generated from vibration source were measured. By using the obtained data, sound speed, root mean square of sound pressure, and frequency were analyzed. Comparing the data of microphones and accelerometers to confirm whether the propagation of sound waves may rely on vibration or not. From the results of experiments, it is revealed that the propagation speed of sound waves is about 160~210m/s and it is getting faster with depth within the depth of 10~40cm. In the Beat tests, the values of root mean square of sound pressure, which received by microphones are attenuating slowly beyond the positions of 45cm away from the sound source. The signals received by the accelerometers have the same tendency.
In addition, speaker tests were performed in this research. Sound, which was recorded from beat test, was made by speaker as sound source, but this sound did not cause apparent vibration in the sand layer during the process of speaker test. From the results of these experiments, it is understood that the sound pressures made by tests decreased rapidly in sand layer, and showed a small stabilized value beyond the positions away from the sound source of 30 cm. It is also proved that soil layer may generate vibration and sound wave due to slide or movement of soil particles. If the generated energy of slide or movement is large enough, the sound wave may transmit away with vibration to a farther distance.

並列關鍵字

sound wave ； vibration wave ； sound speed ； root mean square of sound pressure ； wave propagation

參考文獻

3. 古秉弘，「砂土中音波傳遞與量測之研究」，碩士論文，國立中央大學土木工程學系，中壢(2005)。

4. 李佳龍，「音射定位法於岩石材料之應用」，碩士論文，國立成功大學資源工程學系，第51-58頁，台南(2003)。

5. 吳志鴻，「淺層砂土中音波傳遞特性之研究」，碩士論文，國立中央大學土木工程學系，中壢(2006)。

8. 黃清哲、謝正倫、鄭友誠、尹孝元、許世盛、蔡玫諼，「土石流地聲特性之實驗研究」，中國土木水利工程學刊，第十六卷，第一期，第53-63頁 (2004)。

16. Baker, L.J., and Winbow, G.A., Multipole P-wave logging in formations altered by drilling,” Geophysics, Vol. 53, No. 9, pp. 1207-1218 (1988).